Various systems have been devised and implemented to control the change of gear ratios in a power-shifted transmission. This is generally done with a hydraulic system, including a hydro-mechanical control valve mechanism for modifying the pressure applied to various friction elements in the transmission and to selectively hold and release different components of a planetary gear set. For example, the engine output shaft can be connected to drive the sun gear of such a set, which also includes a plurality of planet gears rotatable on a carrier element and disposed between the sun gear and the outer ring gear. When the ring gear is held against rotation, output drive torque is available from the planet carrier at a first speed ratio. To change ratio, the sun gear is locked to the outer ring gear, which is no longer held against rotation, providing a direct drive connection. This is the operation which occurs in a typical upshift.
A great deal of research has been directed to optimizing the shift "quality". In general, it is not desirable to have a shift of very brief duration, as this produces a jerk by the rapid change in vehicle acceleration, which is very noticeable and found objectionable by most drivers. If the shift time is stretched out for too long a period, undue wear is imposed on the friction elements and other components of the transmission. Therefore, the optimum shift quality occurs somewhere between the too-short time duration, producing the objectionable jerk sensation, and the too-long time duration producing the objectionable component wear.
An electronic control system for accomplishing a proper shift which will have requisite quality is enclosed and claimed in copending application Ser. No. 661,896, filed Feb. 27, 1976 of common assignee.
The object of this invention is to provide a unique control valve which is compatible with the electronic control of the aforementioned application which will result in a compact valve unit which should result in economy of manufacture.